It is known to measure the speed of vehicle wheels by means of sensors and to use the measured speeds to control the wheel slippage. Wheel slippage can be caused by overbraking of wheels (brake slippage), too great a drive torque (drive slippage) or by the drag torque of the engine when the friction coefficient between road and tire is too small. In an ABS, the brake slippage is controlled by changing the brake pressure In a drive slip control (ASR), the drive slippage is controlled by changing the drive torque and/or the brake. In an engine drag torque control, the slippage is controlled by changing the drive.
The tires of a vehicle may have different diameters and thus different wheel speeds can be measured at the individual wheels. This can lead to an inaccuracies in the above mentioned control procedures.
From European patent A2 0133381 to which U.S. Pat. No. 4,566,737 corresponds, it is know to detect during travel different tire diameters by difference formation of wheel speed signals and to correct the measured speed values of wheels with different tire diameters. For controlling purposes, the resulting values can be set into relation to one another.